ROME, Feb 10 (Reuters) - Italian President Giorgio Napolitano faced fierce criticism on Monday over reports that he asked Mario Monti about replacing Silvio Berlusconi as prime minister months before his government fell at the height of the euro zone crisis in 2011.

Berlusconi's Forza Italia party expressed "bitterness and shock" at the reports, based on interviews with Monti and others in a forthcoming book by journalist Alan Friedman, extract of which were published by the Financial Times and the Corriere della Sera newspapers.

Although the events recounted in the book occurred more than two years ago, they risk reopening wounds between the parties that could complicate the already difficult situation facing Prime Minister Enrico Letta's fragile ruling coalition, which is struggling to adopt economic and political reforms.

"We are dismayed to learn that, as early as June 2011, the head of state was actively taking steps to bring down the Berlusconi government and replace him with Mario Monti," the parliamentary floor leaders of Forza Italia, Renato Brunetta and Paolo Romani, said in a statement.

Napolitano has been widely praised outside Italy for his role in helping to navigate the crisis and is seen as a guarantor of stability. But he has faced bitter attacks at home from the anti-establishment 5-Star Movement and many in Berlusconi's camp, who accuse him of overreaching his powers.

Napolitano, who as head of state is responsible for appointing the prime minister, named Monti to lead a technocrat government after Berlusconi resigned during an economic crisis that sent Italy's borrowing costs spiralling out of control and put the future of the euro zone itself in doubt.

In the book, Monti himself confirmed that Napolitano had given him "signals in that direction" as early as June or July, months before Berlusconi's centre-right government fell in November 2011.

Forza Italia senator Augusto Minzolini said his party should consider supporting the impeachment motion against Napolitano launched by the 5-Star Movement last month.

Letta, whom Napolitano appointed to head a coalition of rival parties from the left and right after last year's deadlocked election, issued a statement saying the attacks on the 88-year-old head of state amounted to a "shameful attempt to distort reality".

Napolitano himself dismissed suggestions of a plot to replace Berlusconi as "smoke".

He said he had spoken to Monti frequently during the course of 2011 but noted that Berlusconi's government had only fallen after a split in his own centre-right party and growing tensions with key members of the cabinet including the economy minister at the time, Giulio Tremonti.

The spat over Napolitano's role in appointing Monti comes as Letta's coalition has faced growing pressure to come up with a coordinated reform programme to pull Italy's stagnant economy clear of its longest postwar recession.

On Tuesday, parliament is due to resume debate over a new electoral law intended to avoid the instability and stalemate left by the last election in February which left no side able to form a government and forced the two main rival parties into an uneasy coalition.

On the same day, a Naples court will begin hearing charges that Berlusconi bribed a senator from one of the smaller parties to change sides in 2006 in a bid to bring down the government of former centre-left Prime Minister Romano Prodi, which had a wafer-thin majority and fell two years later. (Editing by Robin Pomeroy)